Geoflow geothermal heating and cooling system principal

Geothermal heating and cooling systems simply move heat from ground to building and generate as much as 4-5 units of heat for every 1 unit of electricity used. Water is circulated inside poly pipes buried in the ground and a small box (heat pump) pumps free heat from ground to the building in hot water (hydronic heating) or heated air (ducted heating). In cooling mode, it works exactly in opposite and takes heat from the building and rejects it to ground. The reason, Geothermal heating and cooling are more efficient is the fact with these systems, we are tapping into the ground as an energy source. The ground has massive thermal mass and its temperature doesn’t change much with seasons.  When the outdoor temperature is freezing, the ground is still 18.5˚C (metro Melbourne) as it was in mid-summer. 

 What makes us different in this field is that GeoFlow Australia is the only geothermal company in Australia with an Australian Certified Geothermal Designer (CGD) . We have the highest qualifications in this industry. Note that geothermal systems are not an off the shelf product and in order to deliver the claimed efficiency, it has to be designed for that.  

 

Different Options for Geothermal Systems

GeoFlow geothermal horizontal heating and cooling system

Horizontal

Horizontal ground pipes in trenches or open pit are usually the most cost-effective when adequate area is available around the building and ground is easy to dig. The most common ground pipes are Slinky…

geoflow geothermal vertical heating and cooling system

Vertical

Vertical geothermal systems are for buildings that have a limited land area available to bury all the geothermal ground pipes in the ground. Set of boreholes are drilled and ground pipes are installed and grouted…

GeoFlow Geothermal water loop heating and cooling system

Water loop

Water loops are innovative use of available bodies of water in close vicinity of the building. Closed loop pipes are submerged into water dams, lakes or ponds to get energy from body of water …

geoflow geothermal open loop heating and cooling system

Open loop

In Open loop systems clean bore water or surface water is directly circulated through the heat pump to transfer energy to/from the available water. The water is returns to the bore or the surface water …

geoflow Energy Piles

Energy piles

Geotechnical structures such as piles, tunnels, sewers, retaining walls and ground slabs can be regarded as ground heat exchanger by simply embedding ground loop pipes in them. Energy Piles are mostly …

We offer a turnkey solution to architects, clients and design teams to deliver high performance buildings. From planning and concept design through to proven operational performance, GeoFlow offers in depth sustainability services that provide valuable assistance throughout the project timeline, reflecting our commitment to efficient performance and our up to date approach.We assist first in minimising the energy requirement via applying the passive solar design concepts and then we introduce the geothermal heating and cooling system as the most efficient heating and cooling systems available (Source). We also provide a design and cost analysis for a conventional heating and cooling system so the client/design team can see the apparent benefits of the geothermal systems.

6-Star Energy Assessment

Horizontal ground pipes in trenches or open pit are usually the most cost-effective when adequate area is available around the building and ground is easy to dig. The most common ground pipes are Slinky…

geoflow geothermal ground heat exchanger design

Geothermal Ground Heat Exchanger Design

We work collaboratively with architects and mechanical design teams to assist with design of the ground pipes (ground heat exchangers) to deliver cost effective geothermal systems with minimum ground works. Mechanical design…

geoflow energy modelling and passive solar house

Passive Solar House

Buildings that are passively designed take advantage of the local climate to maintain thermal comfort. At GeoFlow Australia, we use appropriate strategies and take into account the climate and specifics of the site to quantitatively minimize the heating and cooling …

geoflow hydronic & ducting systems

Hydronic & Ducting

Horizontal ground pipes in trenches or open pit are usually the most cost-effective when adequate area is available around the building and ground is easy to dig. The most common ground pipes are Slinky…

Geothermal Heating Systems Work by Design, not by Accident

Geothermal Heating and Cooling systems, unlike conventional heating and cooling systems, are not an off the shelf products. They have to be designed to run smoothly and efficiently. Here are the steps to make sure your geothermal system is designed and installed correctly, if the person who claims to provide you an efficient geothermal system fails to perform any of the following steps, then something will go wrong at your cost, that’s for sure.

 

1. Building hourly modelling to calculate heating and cooling demand: your geothermal heating systems are sized to match the demand of your specific building. Like any other renewable system (solar PV or solar hot water), it matters what is the heating and cooling demand for every hour in a full year to be satisfied with correctly designed geothermal energy. The reason is that renewable energies are limited to the size of the system and every hour needs to be assessed in computer modelling to make sure energy demand is met with supply in a cost-effective manner. Note that use of rules of thumb always works against the client. The geothermal provider either doesn’t have the capability (which is the case most of the time) or it is not economical for them to do a building modelling and it will be the client to pay for their lack of qualifications.

2. Get your geothermal system designed by a certified geothermal engineer; designing a geothermal system is complicated. That is the beauty of it, there are too many factors to account for to deliver an efficient geothermal system. Rules of thumb can never replace the design procedure. So how a plumber manages to deliver a geothermal system without the required qualifications and accounting for any number? They either overdesign or undersize the geothermal heating system to make sure they won’t be liable for future issues. At the end of the day, it will be a client, who will bury their money for an overdesigned system or get an inefficient geothermal system for undersized geothermal ground loops. Make sure to check the qualifications of your designer. The peak nonprofit organization in charge of geothermal designer certification is IGSHPA and AEE. Go to the below link and search Australia for Certified Geothermal Designer (CGD): https://igshpa.org/business-directory

 

Never trust fake qualifications that are provided by geothermal component manufacturers. There are plenty of them out there and anyone can pay for it and get it in less than a day. 

a. What can go wrong if your geothermal ground loops are undersized?

Most of the time, an unqualified geothermal system installer, undersize and installs fewer pipes in the ground to bring its geothermal cost of installation down and increase their margin. This results in less access to the ground thermal mass which is the source of energy. For instance, in the heating mode of operation, the ground temperature will drops over time (in few weeks or months) and heat pump efficacy will drop to a point it will be less efficient than a conventional split system. Finally, the geothermal compressor will reach to its tripping or it may freeze itself and fracture and all system will stop operating. The cost to fix such a failed system is a major fraction of installing a brand new system.

3. Proper installation, Installation is the easiest part if it is done according to the design criteria. Many people in the US do it as DIY. Make sure that your installer drills down to the right depth and installs the pipes along with all length of borehole or excavation. For instance, drilling can cost as much as $150/m and you have the right to insert a weight and measure the actual depth of the borehole. Pipe insertion into the borehole shall be dome right away after drilling as there can be a collapse in borehole wall which can fill the last few meters of the borehole. Similarly, in a horizontal geothermal layout, the designer might have assumed 8m of pipe to be installed in Slinky mode inside the borehole, inspect pipes and make sure it is installed accordingly. You have all rights to ask questions to make sure the system designed is the one being installed.

4. Before backfilling, ask for results of pressure test and flow test, after backfilling or grouting, it is impossible to make any changes to the ground loops. Your geothermal installer shall flush the pipes of debris and purge them of air at a very specific flow velocity for all different sizes of pipes in the ground. Header pipes are usually the biggest diameter and define the maximum flushing flow rate. If this is not done properly, air will block some of the ground loops and system efficiency will drop. After flushing, the flow and pressure drop in the whole geothermal system shall be measured and compared to the calculations by the geothermal designer. If the actual measurement doesn’t match the calculations that is a sign that there is a blockage somewhere or air is still in the system which needs to be removed. Pressure testing needs to be done both before the backfilling and during the backfill. It allows to identify if there are any leaks in the system to fix them before it’s too late. During backfill, there is also chance of damaging the pipe. Monitoring the pressure locked in the pipes allows to make sure there is no damage to the pipes.

5. Heat pump commissioning and flow rate testing, during operation, a minimum water flow needs to be inside all pipes. This is to make sure water flow in the pipes are in the turbulent regime to extract maximum energy from the ground. These are a simple check that all will need to be assessed against the calculations by the designer. If there is no design in the first place, your plumber might measure something but be sure he has no idea if the measured value is satisfactory or not.

 

Geothermal system components above the ground and after geothermal heat pump are exactly identical to the conventional systems. Unlike geothermal, any mistakes above the ground can be fixed easily as there is easy access to the components. 

Geothermal Heating and Cooling 

Geoflow Geothermal system, Efficient way of Heating and Cooling​Geothermal systems efficiently heat and cool buildings using sustainable geothermal energy accessed via Ground Heat Exchangers (GHEs). In closed loop systems, GHEs comprise pipes embedded in specifically drilled boreholes or trenches or even built into foundations, all within a few tens of metres from the surface. The geothermal systems are just starting to be generally known in Australia with relatively few, but highly varying and diverse installations to date offering a potentially economically viable and environmentally friendly method for heating and cooling of buildings.

However, they require excavation or drilling to bury the GHEs which lead to higher capital costs for installation in comparison with conventional systems. The design of GHEs in Australia is mostly achieved with simple rules of thumb, and simple software that has been developed but not validated for the GHE design.

The high capital cost of GHE installation is one of the main causes preventing wide adoption of direct geothermal systems in Australia. It is therefore imperative that GHEs should be designed as efficiently as possible to minimize the extent and cost of GHE installation.

At GeoFlow Australia, we are using the current design methods together with the design methodology achieved by our head of design team, Dr Amir Kivi through 4 years of research at The University of Melbourne. This is to ensure that the GHE is sized to the needs of the house and to avid under-sizing and over-sizing the heating and cooling system.

Principal Elements of a Geothermal System

The principal elements of a direct geothermal system are shown in figure below

• The heating and cooling demand of the building,
• The Ground Source Heat Pump (GSHP) which causes heat to flow “uphill” from lower temperature to higher temperature,
• The Ground Heat Exchanger (GHE) pipes buried within a few tens of metres of surface as a heat source in winter and heat sink in summer.
A heat transfer fluid (typically water) is circulated through GHE pipes and exchanges heat with the surrounding ground. If the fluid is cooler than the ground, the ground will heat it and if the fluid is hotter than the ground, it will be cooled. GSHPs efficiently upgrade the heat extraction/rejection process. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor heat delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. Read more

The key to the direct geothermal system is that for each kilowatt of electrical energy put into a direct geothermal system, depending on several parameters, about 4 kilowatts of energy is developed for the purposes of heating and cooling. This means that direct geothermal systems could reduce electricity demand for heating and cooling by 75%.  Furthermore, as much of the electrical power in Victoria is generated with brown coal, replacing 75% of the energy used with a clean and free renewable energy source, these systems will have the potential to significantly cut Australia’s carbon footprint.

It is estimated that there are over 3 million direct geothermal systems installed around the world, with the total installed capacity approximately doubling every 5 years since 2000 (Lund et al., 2010). Figure below shows the growth rate of the installed capacity and annual utilization of all forms of geothermal energy for heating and cooling applications (Lund, 2010). In the following, each of the elements of a direct geothermal system is discussed in more detail.

 

utilised energy for heating and cooling from geothermal systemsinstalled capacity of geothermal heating and cooling systems

Types of GHE configuration

Lund (2002), Banks (2008) and Self et al. (2012) provide an excellent overview of different forms of GHEs. Based on their distinctive characteristics, different GHE configurations are classified in Figure ‎below.

Different options of geothermal systems

 

Closed loop GHEs comprise pipes placed in the ground or water through which a fluid circulates and the heat exchange occurs by conduction through the walls of the pipes. Therefore, the fluid remains sealed in the pipes and does not come into contact with the energy storage medium. There are several advantages to this system. One of the main advantages is that there is no problem of contamination either from the loop water entering the ground, or perhaps more critically, from the ground water contaminating the workings of the pumps. 

Horizontal Ground Heat Exchanger

Horizontal trenches are usually the most cost-effective when adequate area is available around the building and trenches are easy to dig. Figure ‎below shows different configurations of horizontal GHE that can be constructed. The horizontal GHE has become increasingly popular due to its low cost and ease of installation. For instance in Canada, about 55% of direct geothermal installations use horizontal GHEs (CGC, 2011). Nevertheless a horizontal GHE requires a large area of ground to lay the pipe network. This problem can be alleviated to some extent by employing a slinky loop arrangement of the pipes. Slinky arrangements are coils of overlapping piping, which are spread out and laid either horizontally or vertically. The first recorded slinky GHE was developed by Bose (1992). This GHE’s ability to focus the area of heat transfer into small volume reduces the length of the trenches by 20-30% of those for single pipe configuration (Wu et al., 2010). The slinky coils can have different lengths per unit length of trench depending on the pitch spacing of successive coils. The performance of slinky coils is similar to straight pipes with an equivalent total length (IGSHPA 2011).

In an urban environment, the ground immediately below a city can be used as a low grade energy storage reservoir. Geotechnical structures such as piles, tunnels, sewers, retaining walls and ground slabs can be regarded as thermo-active structures by simply embedding GHE pipes in them. The literature includes several studies of these thermo-active structures (Adam and Markiewicz, 2009; Xia et al., 2012). For example, if the building is a large commercial or industrial building with significant foundations including large diameter piles, then it is almost certain that these elements will provide the location for the GHE. 

design and installation of Different geothermal heating and cooling systems
Different configurations of horizontal GHE (from IGSHPA (2011), Philippe et al. (2011) and installation at Main Ridge)
(note: the pipes in red are not to scale for better visibility)
geoflow design and installation of Different geothermal heating and cooling systems
Single and stacked multiple pipe

 

 

 

Vertical Ground Heat Exchanger

Geoflow Vertical geothermal heating and cooling solutionWhere there is a confined surface area or minimum disruption of the landscape is desired, Ground Heat Exchangers (GHEs) in form of vertical boreholes (of varying diameter) comprising one or more “U-loops” of high density polyethylene (HDPE) pipe are installed in a borehole backfilled with cement/bentonite grout.

Water Loop Heat Exchanger

Geoflow water Coil Geothermal Heating and cooling SystemWhere there is a body of water in the form of a dam or lake within a reasonable distance from a building, these surface water bodies can also be considered as an energy source.Water loops are gaining popularity because they require no drilling or excavation. These systems, due to an efficient heat exchange interface, potentially require less piping than other GHE configurations. In closed water loops, HDPE coils are attached to a frame and submerged in a water body. The coils are typically supported 0.5m above the lake bottom to allow for convective flow around the piping. Normally the coils should have at least 1.8m of water above them (Self et al., 2012). It is necessary to assure sufficient thermal mass is maintained during low water conditions and prolonged draughts. The CGC (2010) also mentions that in cold climates, if a water body depth is less than 3m, lakes and dams destratify and offer no advantage. Due to flooding and draughts as well as hazards due to moving debris that can damage the GHE, rivers are not ideal for this application.

Open Loop Heat Sources

Geoflow vertical geothermal heating and cooling systemAn open water loop system involves water being removed from the ground or body of water and returned after heat is extracted or added. Clearly, considerable care must be directed at the location of the return system so that the discharge water does not affect the intake temperatures. One of the major advantages of these systems is that relatively large volumes of water can be handled leading to large quantities of heat exchange.

Energy Pile Ground Heat Exchanger

In an urban environment, the ground immediately below a city can be used as a low grade energy storage reservoir. Geotechnical structures such as piles, tunnels, sewers, retaining walls and ground slabs can be regarded as thermo-active structures by simply embedding GHE pipes in them. For example, if the building is a large commercial or industrial building with significant foundations including large diameter piles, then it is almost certain that these elements will provide the location for the GHE.

Ground source Heat Pump (GSHP)

According to the Second Law of Thermodynamics, heat cannot by itself move from a lower temperature to a higher temperature (just as water cannot by itself flow uphill). Heat pumps on the other hand, can move heat from lower temperature to higher temperature regions (just as water pumps can move water uphill). Heat pumps are typically used to transfer the ground’s energy to heat or cool buildings. The principle of a heat pump is illustrated in Figure below for the cooling mode of operation of a water to air heat pump.

The operation of a Ground Source Heat Pump (GSHP) in cooling mode of operation (IGSHPA 1988)


The operation of a Ground Source Heat Pump (GSHP) in cooling mode of operation (IGSHPA 1988)

As shown in Figure ‎above, in cooling mode of operation, water from the ground loops passes through the primary circuit heat exchanger (the condenser) of the heat pump. Here, this water comes into indirect contact with the warmer gas refrigerant. Heat passes from the warmer gaseous refrigerant to the cooler water. As a result of the removal of heat from the refrigerant, it condenses to a liquid phase at a relatively high temperature. When this liquid then passes through an expansion valve, the temperature drops considerably ready to accept heat from the conditioned space. Heat passes from the warmer air from the conditioned space to the liquid refrigerant to cause it to evaporate. The gaseous refrigerant then passes into a compressor where the gas is compressed to significantly increase not only its pressure but also its temperature. The hot gas then passes through the condenser again and the refrigeration cycle continues. Read more

In the cooling mode of operation, the heat generated by the compressor is not useful and together with the heat extracted from the building, should be rejected to ground. In the heating mode of operation, the waste heat generated by the compressor electricity consumption is useful and is rejected to the building to assist in heating. The heat flux delivered at the condenser of a heat pump to the building is the sum of heat flux extracted from the evaporator/GHE and the electric power consumed by the compressor.

The “efficiency” of a heat pump is expressed as a coefficient of performance (CoP). This is defined as the ratio of heat delivered to the building( Qb in kW )

  to electricity consumption of heat pump(QE in kW) : QE in

Why Geothermal?

geoflow australia sustainable energy solutionThe key to the geothermal system is that for each kilowatt of electrical energy put into a geothermal system, depending on several parameters, about 4 to 5 kilowatts of energy is developed for the purposes of heating and cooling. This means that geothermal systems could reduce electricity demand for heating and cooling by 75%. Furthermore, as much of the electrical power in Victoria is generated with brown coal, replacing 75% of the energy used with a clean and free renewable energy source, these systems will have the potential to significantly cut Australia’s carbon footprint.

Geothermal system performance comparison to VRF

It is apparent that due to the thermodynamic advantages of rejecting heat to or extracting heat from the ground rather than the air, Geothermal system has better operational efficiencies, particularly in cold weather and in hot weather. But question is how they compare with conventional systems for a same building.

The ASHRAE headquarters building was refurbished in 2008 and was transformed in to a living lab for assessing the real performance of high efficiency heating and cooling systems in an operational office building environment.

The assessed geothermal system in this study serves a single separate floor and includes 14 individual water-to-air heat pumps (2.6 kW), six 7 kW units and six 10.5 kW heat pumps connected to a ground loop consisting of 122 m deep vertical boreholes, for a total of 111 kW of cooling capacity. The heat pumps have variable Speed fans (driven with electronically commutated motors) with three selected speeds. For the two-year time span of this study, while maintaining similar zone temperatures, the Geothermal system used 98% less total energy than the VRF system, 41% less in the summer cooling season and 172% less in the winter and shoulder seasons. Figure below compares the electric power demand of geothermal system and VRF system side by side.

Geoflow geothermal heating and cooling systems advantages vs variable flow refrigerant VFR systems

Factors contributing to the differences in energy use include: Ground loop water supply temperatures were more favourable than ambient air temperatures for heat pump operation. This allows the GSHP equipment to operate at higher efficiencies. The control strategy of the VRF system resulted in longer runtimes than the GSHP system, especially in mild weather. These longer runtimes coincided with significant amounts of simultaneous cooling and heating in adjacent spaces.

You can read more about this comparison in an article published in ASHRAE Journal

Note that if geothermal system is not designed correctly, a normal off the shelf split air conditioner might be more efficient as it has been engineered in a factory. Hence it is very important to make sure that the geothermal system is 1). Designed correctly and not estimated based on rules of thumb and 2) installed by plumbers under supervision of the same designer.

Hydronic in slab heating

Geoflow Geothermal Hydronic in slab is Efficient way of Heating and Cooling​During the last two decades, radiant floor heating applications have increased significantly. In Germany, Austria and Denmark, 30% to 50% of new residential buildings have floor heating. In Korea, about 90% of residences are heated by underfloor systems.

Indoor air quality

Floor heating also prevents cold corners and due to the higher surface temperatures, there is less chance for condensation and mold growth. The German Allergy and Asthma Association  has produced a study that shows that floor heating reduces the favorable living conditions for house dust mites compared to other heating systems. Higher temperatures in carpets and mattresses decrease the relative humidity. Also, because mites seek the upper areas, they are more easily removed by vacuum cleaners. Another study found a lower level of dust mites in Korean houses than in Japanese houses . This was attributed to the same effect, but was not directly verified.

 

Floor Surface Temperature

In international standards , a floor temperature range of 19°C to 29°C is recommended in the occupied zone for rooms with sedentary and/or standing occupants wearing normal shoes. This is a limiting factor for the capacity of floor systems. For heating, the maximum temperature is 29°C, and for cooling, the minimum temperature is 19°C. In the European standard, it is acceptable to use 35°C as the design floor temperature outside the occupied zone, i.e., within 1 m from outside walls/windows. In spaces where occupants may have bare feet (bathrooms, swimming pools, dressing rooms), the optimal floor temperature for comfort also depends on the floor material.

Design of hydronic system

In the ASHRAE Handbook—HVAC Systems and Equipment (Chapter 5) and in the European standard for floor heating, a method is given to calculate the heating capacity of a floor system. The heat exchange coefficient at design conditions is 11 W/m²·K. At smaller temperature differences between floor surface and space, this will decrease to about 9 W/m²·K. Of the total heat exchange, more than half is due to radiation (~5.5 W/m²·K). The maximum capacity in the occupied zone is about 100 W/m² at 29°C floor temperature and 20°C room temperature. A higher floor temperature like maximum of 35°C may be used within 1 m from the outside walls/windows and for a 20°C room temperature this results in a heat output of 165 W/m². 

 

This maximum heating capacity is independent of the type of floor covering (tiles, wood, carpet). The required water temperature to obtain the maximum heating capacity is, however, dependent on the thermal resistance of the floor covering and other factors such as system type and pipe spacing. The standard lists factors to account for these parameters.